It has long been recognized that hunter's of small game often encounter a wide variety of shots with a shotgun which makes it extremely difficult to successfully bag game. For example, some game, particularly those which have previously been shot at, will try to escape either on the ground or in the air from a distance quite far from the hunter which necessitates a shotshell having a relatively long range effectiveness. On other occasions, similar game may seek to escape on the ground or in the air from a relatively short distance from the hunter, but will seek to escape at a sharp angle relative to the hunter which requires the latter to make "swing shots" which require greater accuracy. It is obvious that the hunter, for the latter situation, would benefit from a shotshell which, at short range, would have a relatively broad pattern of shot pellets in order to successfully bag the game. On the other hand, for the extended range shots, a shotshell having a "tighter pattern" of shot pellets would be more likely to enable the hunter to be successful in bagging the game. This is particularly true because of the fact that shot pellets commence to lose their energy immediately after leaving the muzzle of the gun, which results in the shot pellets fired at long range having lost a substantial amount of their energy. This difficulty is enhanced by the fact that shot pellets will have spread measurably by the time they reach long range distances, so fewer pellets are likely to strike the game or target.
Recent engineering trade-off studies indicate that the ideal balance between the effectiveness of a shotshell and its cost, involves incorporation of low-density shot spread into a wide pattern for shooting close-in targets, while for extended range shots, high-density shot pellets, held into a narrow pattern, are preferable. This is true because a pellet from a shotshell decelerates immediately after being launched from a shotgun and loses energy steadily with distance from the gun. High-density pellets, on the other hand, lose energy more slowly than do lower density pellets of the same diameter and material. Upon being launched at the same size and velocity, they start out with more energy due to greater mass. At any given range, the high-density material pellets will have more energy.
A game bird or other target is vulnerable only to pellets of a certain energy level which is a function of the size of the pellet, its velocity, and its mass. Within a certain range either low-density or high-density material pellets are capable of bringing down a game bird or other target. At greater ranges, however, only high-density pellets are capable of bringing down the same bird because the high-density pellet starts out with more energy and loses it at a slower rate. This is illustrated in FIG. 1 as shown hereinafter.
The pattern of pellets impacting a plane perpendicular to the line of flight of the shot stream is most dense close to the gun and less dense as the stream travels down range. This fact is well known in the art. One can envision this phenomena as a distribution of pellets moving away from the gun within a conical volume of space. "Tighter patterns" are characterized by a smaller cone apex angle. This indicates that close-in targets can be more effectively engaged with a wider pattern of shot, which is desirable. This occurs because at closer ranges, there is a wider pattern of lesser density pellets than of greater density, but there is still a high enough density of pellets per square foot to assure hitting the bird or other target with a sufficient number of pellets to assure downing it, even if not hit by the higher density shot pellets. A more dense pattern at such a close range would only do more damage to the meat of the game without greatly increasing the probability of bagging same. The advantage of the wide pattern at close range is that a bird or other target which is crossing the line of fire at close range requires a very fast sweep of the gun to track it, lead it and down it. This requirement makes proper pointing of the gun more difficult. The wider pattern of the lesser density pellets reduces the difficulty of the shot because it permits a greater miss distance for the center of the pattern with respect to the target, without letting the target get outside the effective pattern area.
Conversely, longer range shots require a tighter pattern spread angle. A loose pattern, suitable for close range work, results in a great separation between pellets at longer ranges. This markedly increases the possibility of missing the target with all of the pellets or else hitting the target with too few pellets to be effective. A tighter cone angle is needed to make a sufficiently high density of pellets in the pattern at long range. Thus, it can be seen that a wide distribution cone angle is best at close range and a narrow distribution cone angle is best at longer range.
Retained energy within the shot pellets is important at extended range and less so at short range. A lesser degree of retained energy is acceptable at short range, because it is far more likely at short range to have a greater concentration of pellets and will have higher velocity. The energy of the pellets at the muzzle of the shotgun is a function of their velocity and mass.
The velocity will be limited by the amount of propellant and the total mass of pellets. For a given amount of a selected propellant, the more mass that the pellets have, the lower the velocity will be. The system is muzzle energy constrained. Thus, it is not feasible to increase the number of pellets or the mass of the individual pellets without limit. The trade-off is between a large number of low-density pellets that are effective primarily at short range on one hand, or a relatively small number of high-density pellets which are effective at longer ranges, but less so at short range because of their limited number.
Game bird or other targets may present a shooting opportunity at either short, long, or intermediate range and the hunter does not have time to switch shells quickly enough to adjust to the situation at hand. The hunter will be best served by a shell which is effective at all ranges, including ranges that can not be attained by steel shot. Our invention provides an advantageous combination of short and long range effects.
The cost of the shell would depend in part on the cost per pound of the pellets and the number and size of any type of pellets employed. Higher density non-toxic shot pellets tend to be more expensive than low-density pellets such as steel. There is a fairly complex relationship between pellet material and size, propellant, velocity, pattern density, cost and effectiveness.
We have found that an excellent solution to all of the above considerations is to use both low and high density pellets in the same shotshell. An example would be to use tungsten-based shot pellets and steel shot pellets in combination. Other combinations, such as tungsten particles embedded in a polymer, can be used to advantage as well. Because of their relatively low density, a given number of steel pellets weigh less than the same size and number of pellets of a higher density material, and provides a higher velocity at all ranges exceeding zero. For a fixed number of pellets, higher density pellets of the same size increase the mass of pay load and reduce the maximum muzzle velocity. The tungsten-based or other high-density material pellets provide the ability to reach out farther in range, beyond the effective range of the steel pellets. To most effectively accomplish this, the high-density pellets should be limited, if possible, to a narrow distribution cone angle so as to maintain a sufficient pattern density at the extended range The steel pellets, on the other hand, should be spread over a wider pattern to increase the probability of hitting the game or other target at close range. Furthermore, by combining more expensive tungsten (or other high-density) pellets with much lower cost steel pellets, the cost of the product can be maintained at a lower level than can be accomplished with the same total number of high-density pellets, because of the typically high cost of high-density pellet materials The highest effective ranges of lead, steel, and tungsten are: lead 150-160 ft, steel 125 ft, and tungsten 160 ft. Tungsten is lighter than lead, but it holds its shape better and patterns better, so it performs better than lead. Our invention takes advantage of these phenomena.